Access to Service Bus message application properties for trigger and output

When using the `spring-cloud-azure-starter-servicebus` library for regular Spring Boot applications you can use the wrapper class `ServiceBusMessage` to get and set the application properties (`message.getApplicationProperties().put("key", "value")`, for example).

But when I setup an Azure Function I have found no way to either get application properties from incoming message, nor being able to set it for outgoing messages.
```java
@Component
public class UppercaseFunction {

@FunctionName("uppercase")
public void run(
@ServiceBusQueueTrigger(/* config */) String message,
@ServiceBusQueueOutput(/* config */) OutputBinding output) {
// How would I read application properties from the incoming message?
output.setValue(message.toUpperCase());
// How would I set application properties on the outgoing message?
}
}
```

Have I missed some part of the documentation or is this not supported?